Using the instructions from this site, I have started cutting up plastic grocery bags and knitting them into a reusable bag.
My reusable shopping bag obsession is beginning to take over my life! The only problem is that it takes several plastic bags to make one reusable bag (I'm on my third already), so ironically I need more plastic to save the environment.
I'm having lots of fun, though, and maybe I'll get good enough to sell them at a craft stall or something. You never know!